Which setting should the fuel selector valve be in for takeoff in a Cessna 172?

For takeoff in a Cessna 172, the fuel selector valve should be set to "Both tanks." This setting ensures that the engine has access to fuel from both the left and right fuel tanks, maximizing the availability of fuel and ensuring proper fuel flow to the engine during critical phases of flight such as takeoff.

Selecting "Both tanks" helps to balance the fuel load, which is particularly important since fuel imbalance can affect the aircraft's handling and performance. By using both tanks, pilots minimize the risk of running out of fuel from either tank prematurely, which could occur if only one tank were selected and its fuel supply was depleted.

This procedure also helps to maintain consistent performance, reducing the chance of fuel starvation or engine failure due to fuel supply issues.